Why are teratogens so difficult to study?
• have effects only during selective time windows • may have different effects at different times • effects from exposure to several teratogens may interact in complex ways • relation between dosage and outcome problem • sleeper effects • correlated variables Behavioural milestones of fetal development 6-8 weeks • heart beat by 4 weeks • reflexive movement • brainstem activity by 10 weeks • movement — can bend trunk & neck, rotate pelvis, extend upper arms down & back, open jaw • reflexive response to touch (1st reflex) • all reflexes of the newborn except breathing and crying have developed by 4 months 5-7 months • cortical brain waves EEG (all neurons are formed) • active cyclic movements • eyes sensitive to light • hearing — structurally mature at 6 months: startle reaction to very loud sounds (heart rate, kicking, etc.) • vestibular sense (structurally and functionally mature by 6 months) • memory — habituation to repeated sounds and recovery to new sound (7 months) near term •
